The condensation reaction of an olefin or a mixture of olefins over an acid catalyst to form higher molecular weight products is a widely used commercial process. This type of condensation reaction may be referred to as an oligomerization reaction, and the products are generally low molecular weight oligomers that are formed by the condensation of up to 12, typically 2, 3, or 4, but up to 5, 6, 7, or even 8 olefin molecules with each other. For example, low molecular weight olefins (such as, for example, propene, 2-methylpropene, 1 -butene, 2-butenes, pentenes, and hexenes) may be converted by oligomerization processes using zeolite catalysts to a produce oligomers. Exemplary uses of such oligomers include high-octane gasoline blending stocks, starting material for the production of chemical intermediates, and other end-products. Such chemical intermediates and end-products include alcohols, acids, detergents, and esters such as plasticizer esters and synthetic lubricants.
Industrial oligomerization processes employing zeolite catalysts typically run for several weeks before a catalyst change is required or a decommissioning of the reactor is needed. In industrial processes, zeolite catalysts are generally delivered as an extrudate of the zeolite catalyst and a binder. Extrudates may have many shapes and may be distinguished by their shape or number of lobes of each extrudate, for example, cylindrical (solid or hollow), trilobe, quadrulobe, (or simply multilobe).
The feedstocks for the reactions are generally obtained from refining activities such as a stream derived from catalytic or steam cracking that may have been subjected to fractionation. The nature of such refining activities is such that there will be variations in the constituents of the feedstocks. In addition, it may be desirable to change the nature of the feed during a reactor run. Thus, the catalyst activity and the reaction conditions vary according to the composition of the feedstock. As a result, the ideal catalyst provides not only the ability to run a long time as referred to in terms of catalyst life, catalyst activity, or catalyst stability but is also able to oligomerize selectively to produce desired end products using a variety of heterogeneous feedstocks that may contain isomers, poisons, and saturated and unsaturated molecules. Furthermore, the reactions are exothermic and the size of the exotherm also depends upon the nature and amount of the constituents of the feedstock. For example, if isobutylene and propylene are present, they are particularly reactive generating a large amount of heat of reaction.
The high temperatures generated may lead to carbonaceous deposits on the catalyst caused by a build up of condensed, heavy hydrocarbons similar to asphalt. Such deposits are commonly termed “coke” and lead to deactivation of the zeolite catalyst. In general, the higher the concentration of olefin in the feed, the higher will be the rate of heat release from the catalyzed reaction, and thus, the higher the temperatures reached. Consequently, there will be a higher rate of coke formation and deposition of coke on the catalyst particle. As a result, this has placed a limit on the maximum concentration of olefin that can be tolerated in the feed.
Useful feed streams containing olefins such as C3 and C4 olefins may be refinery streams derived from steam cracking or catalytic cracking and the composition of the stream will depend upon the raw material from which it is produced and the production technology employed. For example, propylene refinery streams may typically contain up to 75 wt % propylene with the balance being predominantly propane. Similarly butene refinery streams may typically contain up to 70 wt % butenes with the balance being predominantly butanes. Poisons, such as, for example, nitrogen containing compounds (e.g., nitrites) and sulfur containing compounds, and isomeric equivalents are also most likely present. Thus, the reactivity of the olefins in oligomerization processes with zeolite catalysts varies according to the nature of the olefin, its concentration in the feedstock, and other variable constituents.
Background references include U.S. Pat. Nos. 3,960,978, 4,016,218, 4,021,502 4,381,255, 4,560,536, 4,919,896, 5,446,222, 5,464,593, 5,672,800, 6,143,942, 6,403,853, 6,517,807, 6,884,914, 7,374,662, U.S. Patent Application Publication Nos. 2005/0054516, 2006/0199987, 2009/0216056, EP 0 220 933 A. EP 746 538 A, EP 2 095 866 A, WO 1994/12452, WO 2005/118512, WO 2005/118513, WO 2007/006398, WO 2008/088452, GB 1 418 445 A, JP 2004 238209 A, Interaction of Acetonitrile with Olefins and Alcohols in Zeolite H-ZSM-5: In Situ Solid-State NMR Characterization of the Reaction Products, Alexander G. Stepanov, Mikhail V. Luzgin, Chem. Eur. J., 1997, 3, No. 1, pp. 47-56, and Analysis of Coke Deposition Profiles in Commercial Spent Hydroprocessing Catalysts Using Raman Spectroscopy, Bas M. Vogelaar et al. Fuel 86 (2007), pp. 1122-1129.
Therefore, there remains a need for improvements in particles comprising zeolite catalysts that provide for extended production runs yielding desired end products. Additionally, there remains a need for the particles to be able to oligomerize in presence of higher concentrations of catalyst poisons and yet yield higher concentrations of the desired end product. It will be appreciated that in large scale industrial processes, small increases in production (such as ≥1%) have highly significant value.